As a charging system for non-aqueous secondary batteries, the system as described in FIG. 24 has been so far widely known. According to the system, a DC voltage Vin outputted from an AC adapter 30 is supplied to portable equipment 20, wherein the DC voltage is fed to a charging DC/DC converter that performs as a constant-voltage and constant-current power supply and charges non-aqueous secondary batteries in a battery pack 10 by supplying a charging current I CHG.
A battery voltage V Batt of the non-aqueous secondary batteries in the battery pack 10 is built up by charging according to the characteristic curve as shown in FIG. 25. More specifically, a constant-current charging takes place until the battery voltage V Batt reaches usually a constant battery control voltage Vc, and after the battery voltage V Batt has reached the battery control voltage Vc in value constant-voltage charging takes over so that the battery voltage V Batt may not exceed the battery control voltage Vc. Once the constant-voltage charging has started, the charging current I CHG starts declining. This declining status is detected by a current detecting means and when the charging current has reached a specified value the output of the DC/DC converter is shut off by a control means and the charging operation is ended. Thus the charging of non-aqueous secondary batteries has been so far performed.
The prior art charging system for non-aqueous secondary batteries, however, requires a charging DC/DC converter that is able to output a high accuracy charge control voltage Vc, resulting in a problem of ending up with high costs.
Instead of using the foregoing charging DC/DC converter, use of a dropper type constant-voltage control circuit is proposed to reduce the high costs of the above system, but a large amount of heat generated from the dropper type constant-voltage control circuit has presented another problem.
Furthermore, in the case wherein a charge control is conducted inside of a battery pack, it is impossible for the foregoing charging DC/DC converter to be built in a battery pack from the points of both costs and dimensions (components count) and it is impossible again for the dropper type constant-voltage control circuit to be contained inside of a battery pack when adverse effects imposed on the batteries and other electronic components by the large amount of heat generated from the dropper type circuit are considered, thereby presenting still another problem.
The present invention deals with the foregoing problems that have been so far existing and the object thereof is to provide a pulse charging method and charging system for non-aqueous secondary batteries that are inexpensive, no heat generating and capable of reducing a charge time. The present invention also aims at providing a pulse charging method for non-aqueous secondary batteries that allows a charging system to be built in a battery pack.